The invention relates to fuel injection valves for internal combustion engines, of the type comprising a hollow body defining a circuit for fuel under pressure communicating with the outside through a passage bounded by a valve seat and comprising a closure member movable in the body between a position of abutment against the valve seat, towards which it is spring biased, and a position for which the valve is open, determined by a fixed stop, towards which it is pulled by a winding located in the body when the winding is energized.
The invention is of particular, although not exclusive interest, in fuel supplying systems of the type called "monopoint" injection comprising one or several valves opening into the air intake of the engine. In these valves, fuel is injected under moderate pressure, very much less than the pressure required for direct introduction into the combustion chambers of the engine.
Many valves of the above-defined type are already known. In most cases, the valve seat, fast with the body, defines a central aperture and the fuel injection passage is bounded by this seat and a needle placed along the axis of the seat. At rest, a spring applies the needle onto the seat. When the winding is energized, pressurized fuel is delivered in the form of a jet which divides into droplets. However, particularly when injection is at low pressure, the size of the droplets and their distribution in the airflow are difficult to adjust with accuracy.
Attempts have been made to obtain better results by providing the needle with a downwardly flared frustoconical end portion, opening outwards. It is thus expected to achieve fuel distribution in the air passage as a flat conical jet, more favorable to good distribution than a concentrated jet. While at first glance that solution may be thought as simple as that involving an opening inward movement, it presents in fact various drawbacks. The operation is reversed as compared with regular valves; the needle must project through the seat opening, which complicates valve assembling; the pressure exerted by the fuel tends to open the valve, whence an increased risk of leakage of fuel.
It is an object of the invention to provide an improved injection valve of the above-defined type; it is a more specific object to provide an injection valve delivering a highly flared conical jet without however raising difficulties of mechanical construction.
For that purpose, there is provided an injection valve whose closure member is carried by an annular part slidably received on a fixed axial guide whose outward end portion is enlarged and has a flared surface acting as a valve seat.
The annular part is formed with ports for fuel flow from inside the valve body toward the flared surface and toward the gap which appears between the closure member and the seat when the closure member is lifted from the seat upon energization of the winding.
The annular part may comprise a core or plate of ferromagnetic material positioned so as to be subjected to the action of the magnetic field of the control winding.
It would seem, at first sight, that this solution is to be rejected, due to the fact that it requires the insertion, between the body and the closure member, of a sliding seal. In fact, that drawback has proven non existent and it has been found that the fluid-tight seal could withstand a very large number of openings and closing without premature wear. That favorable result is probably due to the very short strokee of the closure member: the movements of small amplitude of the closure member do not result into a sliding movement on the seal but is taken by deformation of the latter, at least when the seal has a sufficient freedom of movement; that condition is fulfilled when the seal is a O-ring housed in a groove of sufficient axial development of the body.
The invention will be better understood on reading the following description of a valve for use in a "monopoint" injection system for a combustion engine, which constitutes a particular embodiment of the invention given by way of example only.